1. Field of the Invention
The present invention relates to methods of cementing subterranean zones utilizing foamed or non-foamed cement compositions having improved rheology, fluid loss control and set retardation.
2. Description of the Prior Art
Foamed and non-foamed hydraulic cement compositions are often utilized in cementing subterranean zones penetrated by well bores. For example, foamed and non-foamed cement compositions are used in primary well cementing operations whereby strings of pipe such as casing and liners are cemented in well bores. In performing primary cementing, a cement composition is pumped into the annular space between the walls of a well bore and the exterior surfaces of a pipe string disposed therein. The cement composition is permitted to set in the annular space thereby forming an annular sheath of hardened substantially impermeable cement therein. The cement sheath physically supports and positions the pipe string in the well bore and bonds the exterior surfaces of the pipe string to the walls of the well bore whereby the undesirable migration of fluids between zones or formations penetrated by the well bore is prevented.
The foamed and non-foamed cement compositions utilized for cementing in subterranean zones penetrated by well bores must have good rheological properties, low fluid losses and sufficient set retardation at high temperatures. In addition, the cement compositions must have adequate thickening times and compressive strengths. Heretofore, carboxymethylhydroxyethylcellulose (CMHEC) has been used in foamed and non-foamed cement compositions to control fluid loss and provide set retardation to the cement compositions. While CMHEC has been used successfully as an additive in cement compositions used for cementing subterranean zones, there are continuing needs for improved cementing methods, cement compositions and cement additives for providing improved rheologies, viscosities, fluid loss control properties, thickening times and compressive strengths to cement compositions placed in subterranean zones.
The present invention provides improved methods, cement compositions and additives for cementing subterranean zones penetrated by well bores which meet the needs described above and overcome the deficiencies of the prior art. The improved methods of this invention are basically comprised of the following steps. A cement composition is prepared or provided comprised of a hydraulic cement, sufficient water to form a slurry and an additive for providing improved rheology, fluid loss control and set retardation to the cement composition comprised of carboxymethylhydroxyethylcellulose having in the range of from about 0.62 to about 2.21 moles of hydroxyethyl substitution and in the range of from about 0.44 to about 0.52 degrees of carboxymethyl substitution, and a 2% by weight aqueous solution of the carboxymethylhydroxyethylcellulose has a Hxc3x6ppler viscosity in the range of from about 55 mPa.s to about 359 mPa.s. Thereafter, the cement composition is placed in a subterranean zone and allowed to set into a solid mass therein.
An improved cement composition for cementing in a subterranean zone is also provided by this invention. The improved cement composition is comprised of a hydraulic cement, sufficient water to form a slurry and an additive for providing improved rheology, fluid loss control and set retardation to the cement composition comprised of carboxymethylhydroxyethylcellulose having in the range of from about 0.62 to about 2.21 moles of hydroxyethyl substitution, and in the range of from about 0.44 to about 0.52 degrees of carboxymethyl substitution and a 2% by weight aqueous solution of the carboxymethylhydroxyethylcellulose has a Hxc3x6ppler viscosity in the range of from about 55 mPa.s to about 359 mPa.s.
An improved cement composition additive for providing improved rheology, fluid loss control and set retardation to a cement composition is comprised of carboxymethylhydroxyethylcellulose having in the range of from about 0.62 to about 2.21 moles of hydroxyethyl substitution and in the range of from about 0.44 to about 0.52 degrees of carboxymethyl substitution, and a 2% by weight aqueous solution of the carboxymethylhydroxyethylcellulose has a Hxc3x6ppler viscosity in the range of from about 55 mPa.s to about 359 mPa.s.
The objects, features and advantages of the present invention will be readily apparent to those skilled in the art upon a reading of the description of preferred embodiments which follows.
As mentioned above, carboxymethylhydroxyethylcellulose (hereinafter referred to as CMHEC) has heretofore been used as a set retarder and fluid loss control additive in foamed and non-foamed cement compositions. While the use of CMHEC has improved the rheology of the prior cement compositions and provided some fluid loss control and set retardation properties thereto, improved such properties are needed particularly in subterranean zones having temperatures in the range of from about 110xc2x0 F. to about 220xc2x0 F.
It has been discovered that CMHEC with a particular ethylene oxide substitution and a particular carboxymethyl substitution provides a much improved additive for foamed and non-foamed cement compositions. That is, the foamed and non-foamed cement compositions of the present invention which include CMHEC having in the range of from about 0.62 to about 2.21 moles of hydroxyethyl substitution and in the range of from about 0.44 to about 0.52 degrees of carboxymethyl substitution have enhanced properties as compared to prior CMHEC additives. That is, the cement compositions of this invention have superior rheology, fluid loss control properties, thickening times and compressive strengths as compared to the prior art cement compositions.
An improved method of this invention is comprised of the following steps. A cement composition is prepared or provided comprised of a hydraulic cement, sufficient water to form a slurry and an additive for providing improved rheology, fluid loss control and set retardation to the cement composition comprised CMHEC having in the range of from about 0.62 to about 2.21 moles of hydroxyethyl substitution and in the range of from about 0.44 to about 0.52 degrees of carboxymethyl substitution, and a 2% by weight aqueous solution of the CMHEC has a Hxc3x6ppler viscosity in the range of from about 55 mPa.s to about 359 mPa.s.
An improved cement composition of this invention is comprised of a hydraulic cement, sufficient water to form a slurry and an additive for providing improved rheology, fluid loss control and set retardation to the cement composition comprised of CMHEC having in the range of from about 0.62 to about 2.21 moles of hydroxyethyl substitution and in the range of from about 0.44 to about 0.52 degrees of carboxymethyl substitution, and a 2% by weight aqueous solution of the CMHEC has a Hxc3x6ppler viscosity in the range of from about 55 mPa.s to about 359 mPa.s. The CMHEC of this invention is present in the cement composition in an amount in the range of from about 0.1% to about 2.5% by weight of the hydraulic cement therein.
The Hxc3x6ppler viscosity measurement in units of milliPascal.seconds (mPa.s) is determined using a Falling Ball Viscometer. In the use of such a viscometer, a fluid sample (the viscosity of which is to be measured) is placed in a tilted glass measuring tube surrounded by a jacket to allow accurate temperature control by means of a constant temperature circulator. The tube is positioned at a 10xc2x0 inclination with respect to the vertical. The tube has two ring marks spaced apart by 100 millimeters. A ball is allowed to fall through the fluid sample. Falling from a starting position at the top of the tube, the ball accelerates along a distance to reach a steady-state speed providing a uniform shear flow of the liquid in a sickle shape gap in the tube surrounding the ball. The time for the ball to pass between the ring marks on the tube is measured. The time is then used to calculate viscosity in the absolute units of mPa.s.
The hydraulic cement in the cement composition is selected from the group consisting of Portland cements, slag cements, pozzolana cements, gypsum cements, alumina cements and alkaline cements. Of these, Portland cement is preferred.
The water in the cement composition is selected from the group consisting of fresh water and salt water. The term xe2x80x9csalt waterxe2x80x9d is used herein to mean unsaturated salt solutions and saturated salt solutions including brines and seawater. The water is present in the cement composition in an amount in the range of from about 35% to about 55% by weight of hydraulic cement therein.
A foamed cement composition of this invention is comprised of a hydraulic cement, sufficient water to form a slurry and a CMHEC additive of this invention as described above. In addition, the foamed cement composition includes sufficient gas therein to foam the cement slurry and a sufficient amount of a foaming and foam stabilizing surfactant mixture to facilitate the formation of and stabilize the foam. As mentioned above in connection with the non-foamed cement composition, various cements can be utilized with Portland cement being preferred. The water in the cement composition can be fresh water or salt water and is present in the foamed composition in an amount in the range of from about 35% to about 55% by weight of hydraulic cement therein.
The gas in the foamed cement composition can be air or nitrogen, with nitrogen being preferred.
A particularly suitable and preferred mixture of foaming and foam stabilizing surfactants for use in accordance with this invention is comprised of an ethoxylated alcohol ether sulfate surfactant of the formula H(CH2)a(OC2H4)bOSO3NH4+ wherein a is an integer in the range of from about 6 to about 10 and b is an integer in the range of from about 3 to about 10; an alkyl or alkene amidopropylbetaine surfactant having the formula Rxe2x80x94CONHCH2CH2CH2N+(CH3)2CH2CO2xe2x88x92 wherein R is a radical selected from the group of decyl, cocoyl, lauryl, acetyl and oleyl; and an alkyl or alkene amidopropyldimethylamine oxide surfactant having the formula Rxe2x80x94CONHCH2CH2CH2N+(CH3)2Oxe2x88x92 wherein R is a radical selected from the group of decyl, cocoyl, lauryl, acetyl and oleyl. The ethoxylated alcohol ether sulfate surfactant is generally present in the additive in an amount in the range of from about 60 to about 64 parts by weight, and more preferably in an amount of about 63.3 parts by weight. The alkyl or alkene amidopropylbetaine surfactant is generally present in the additive in an amount in the range of from about 30 to about 33 parts by weight, and more preferably in an amount of 31.7 parts by weight. The alkyl or alkene amidopropyldimethylamine oxide surfactant is generally present in the additive in an amount in the range of from about 3 to about 10 parts by weight, and more preferably in an amount of about 5 parts by weight. The additive can be in the form of a mixture of the above described surfactants, but more preferably, the additive includes fresh water in an amount sufficient to dissolve the surfactants to more easily be combined with the cement composition. The mixture of foaming and foam stabilizing surfactants is generally included in the cement composition in an amount in the range of from about 0.8% to about 5% by volume of water in the composition, and more preferably in an amount of about 2%.
The improved cement composition additives of this invention for providing improved rheology, fluid loss control and set retardation to cement compositions are generally comprised of CMHEC having in the range of from about 0.62 to about 2.21 moles of hydroxyethyl substitution and in the range of from about 0.44 to about 0.52 degrees of carboxymethyl substitution, and a 2% by weight aqueous solution of the CMHEC has a Hxc3x6ppler viscosity in the range of from about 55 mPa.s to about 359 mPa.s.
A particularly preferred additive of this invention for providing improved rheology, fluid loss control and set retardation to foamed or non-foamed cement compositions useful in cementing subterranean zones is comprised of CMHEC having about 1.93 moles of hydroxyethyl substitution and about 0.52 degrees of carboxymethyl substitution, and a 2% by weight aqueous solution of the CMHEC has a Hxc3x6ppler viscosity of about 55 mPa.s.
A preferred method of this invention for cementing a subterranean zone is comprised of the steps of: (a) providing or preparing a cement composition comprised of a hydraulic cement, sufficient water to form a slurry and an additive for providing improved rheology, fluid loss control and set retardation to the cement composition comprised of CMHEC having in the range of from about 0.62 to about 2.21 moles of hydroxyethyl substitution and in the range of from about 0.44 to about 0.52 degrees of carboxymethyl substitution, and a 2% by weight aqueous solution of the CMHEC has a Hxc3x6ppler viscosity in the range of from about 55 mPa.s to about 359 mPa.s; (b) placing the cement composition in the subterranean zone; and (c) allowing the cement composition to set into a solid mass therein.
Another preferred method of this invention for cementing a subterranean zone is comprised of the steps of: (a) providing a foamed cement composition comprised of Portland cement, sufficient water to form a slurry, an additive for providing improved rheology, fluid loss control and set retardation to the cement composition comprised of CMHEC having in the range of from about 0.62 to about 2.21 moles of hydroxyethyl substitution and in the range of from about 0.44 to about 0.52 degrees of carboxymethyl substitution and a 2% by weight aqueous solution of the CMHEC has a Hxc3x6ppler viscosity in the range of from about 55 mPa.s to about 359 mPa.s, sufficient gas to foam the slurry and a sufficient amount of a foaming and foam stabilizing surfactant mixture to facilitate the formation of and stabilize the foam; (b) placing the cement composition in the subterranean zone; and (c) allowing the cement composition to set into a solid mass therein.
An improved cement composition of this invention for cementing in a subterranean zone is comprised of: a hydraulic cement; sufficient water to form a slurry; and an additive for providing improved rheology, fluid loss control and set retardation to the composition comprised of CMHEC having in the range of from about 0.62 to about 2.21 moles of hydroxyethyl substitution and in the range of from about 0.44 to about 0.52 degrees of carboxymethyl substitution, and a 2% by weight aqueous solution of the CMHEC has a Hxc3x6ppler viscosity in the range of from about 55 mPa.s to about 359 mPa.s.
An improved cement composition additive of this invention for providing improved rheology, fluid loss control and set retardation to cement compositions is generally comprised of CMHEC having in the range of from about 0.62 to about 2.21 moles of hydroxyethyl substitution and in the range of from about 0.44 to about 0.52 degrees of carboxymethyl substitution, and a 2% by weight aqueous solution of the CMHEC has a Hxc3x6ppler viscosity in the range of from about 55 mPa.s to about 359 mPa.s.